MFC r309124:

Upgrade our copies of clang, llvm, lldb, compiler-rt and libc++ to 3.9.0
release, and add lld 3.9.0.  Also completely revamp the build system for
clang, llvm, lldb and their related tools.

Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
support to build; see UPDATING for more information.

Release notes for llvm, clang and lld are available here:
<http://llvm.org/releases/3.9.0/docs/ReleaseNotes.html>
<http://llvm.org/releases/3.9.0/tools/clang/docs/ReleaseNotes.html>
<http://llvm.org/releases/3.9.0/tools/lld/docs/ReleaseNotes.html>

Thanks to Ed Maste, Bryan Drewery, Andrew Turner, Antoine Brodin and Jan
Beich for their help.

Relnotes:	yes

MFC r309147:

Pull in r282174 from upstream llvm trunk (by Krzysztof Parzyszek):

  [PPC] Set SP after loading data from stack frame, if no red zone is
  present

  Follow-up to r280705: Make sure that the SP is only restored after
  all data is loaded from the stack frame, if there is no red zone.

  This completes the fix for
  https://llvm.org/bugs/show_bug.cgi?id=26519.

  Differential Revision: https://reviews.llvm.org/D24466

Reported by:    Mark Millard
PR:             214433

MFC r309149:

Pull in r283060 from upstream llvm trunk (by Hal Finkel):

  [PowerPC] Refactor soft-float support, and enable PPC64 soft float

  This change enables soft-float for PowerPC64, and also makes
  soft-float disable all vector instruction sets for both 32-bit and
  64-bit modes. This latter part is necessary because the PPC backend
  canonicalizes many Altivec vector types to floating-point types, and
  so soft-float breaks scalarization support for many operations. Both
  for embedded targets and for operating-system kernels desiring
  soft-float support, it seems reasonable that disabling hardware
  floating-point also disables vector instructions (embedded targets
  without hardware floating point support are unlikely to have Altivec,
  etc. and operating system kernels desiring not to use floating-point
  registers to lower syscall cost are unlikely to want to use vector
  registers either). If someone needs this to work, we'll need to
  change the fact that we promote many Altivec operations to act on
  v4f32. To make it possible to disable Altivec when soft-float is
  enabled, hardware floating-point support needs to be expressed as a
  positive feature, like the others, and not a negative feature,
  because target features cannot have dependencies on the disabling of
  some other feature. So +soft-float has now become -hard-float.

  Fixes PR26970.

Pull in r283061 from upstream clang trunk (by Hal Finkel):

  [PowerPC] Enable soft-float for PPC64, and +soft-float -> -hard-float

  Enable soft-float support on PPC64, as the backend now supports it.
  Also, the backend now uses -hard-float instead of +soft-float, so set
  the target features accordingly.

  Fixes PR26970.

Reported by:	Mark Millard
PR:		214433

MFC r309212:

Add a few missed clang 3.9.0 files to OptionalObsoleteFiles.

MFC r309262:

Fix packaging for clang, lldb and lld 3.9.0

During the upgrade of clang/llvm etc to 3.9.0 in r309124, the PACKAGE
directive in the usr.bin/clang/*.mk files got dropped accidentally.

Restore it, with a few minor changes and additions:
* Correct license in clang.ucl to NCSA
* Add PACKAGE=clang for clang and most of the "ll" tools
* Put lldb in its own package
* Put lld in its own package

Reviewed by:	gjb, jmallett
Differential Revision: https://reviews.freebsd.org/D8666

MFC r309656:

During the bootstrap phase, when building the minimal llvm library on
PowerPC, add lib/Support/Atomic.cpp.  This is needed because upstream
llvm revision r271821 disabled the use of std::call_once, which causes
some fallback functions from Atomic.cpp to be used instead.

Reported by:	Mark Millard
PR:		214902

MFC r309835:

Tentatively apply https://reviews.llvm.org/D18730 to work around gcc PR
70528 (bogus error: constructor required before non-static data member).
This should fix buildworld with the external gcc package.

Reported by:	https://jenkins.freebsd.org/job/FreeBSD_HEAD_amd64_gcc/

MFC r310194:

Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
3.9.1 release.

Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
support to build; see UPDATING for more information.

Release notes for llvm, clang and lld will be available here:
<http://releases.llvm.org/3.9.1/docs/ReleaseNotes.html>
<http://releases.llvm.org/3.9.1/tools/clang/docs/ReleaseNotes.html>
<http://releases.llvm.org/3.9.1/tools/lld/docs/ReleaseNotes.html>

Relnotes:	yes

1 files changed, 1500 insertions, 0 deletions

diff --git a/contrib/llvm/tools/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp b/contrib/llvm/tools/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
new file mode 100644
index 0000000..f3e1596
--- /dev/null
+++ b/contrib/llvm/tools/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
@@ -0,0 +1,1500 @@
+//===- lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp ---------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+///
+/// \file For mach-o object files, this implementation converts normalized
+/// mach-o in memory to mach-o binary on disk.
+///
+///                 +---------------+
+///                 | binary mach-o |
+///                 +---------------+
+///                        ^
+///                        |
+///                        |
+///                  +------------+
+///                  | normalized |
+///                  +------------+
+
+#include "MachONormalizedFile.h"
+#include "MachONormalizedFileBinaryUtils.h"
+#include "lld/Core/Error.h"
+#include "lld/Core/LLVM.h"
+#include "llvm/ADT/ilist.h"
+#include "llvm/ADT/ilist_node.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/Format.h"
+#include "llvm/Support/Host.h"
+#include "llvm/Support/MachO.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/raw_ostream.h"
+#include <functional>
+#include <list>
+#include <map>
+#include <system_error>
+
+using namespace llvm::MachO;
+
+namespace lld {
+namespace mach_o {
+namespace normalized {
+
+struct TrieNode; // Forward declaration.
+
+struct TrieEdge : public llvm::ilist_node<TrieEdge> {
+  TrieEdge(StringRef s, TrieNode *node) : _subString(s), _child(node) {}
+
+  StringRef          _subString;
+  struct TrieNode   *_child;
+};
+
+} // namespace normalized
+} // namespace mach_o
+} // namespace lld
+
+
+namespace llvm {
+  using lld::mach_o::normalized::TrieEdge;
+  template <>
+  struct ilist_traits<TrieEdge>
+    : public ilist_default_traits<TrieEdge> {
+  private:
+    mutable ilist_half_node<TrieEdge> Sentinel;
+  public:
+    TrieEdge *createSentinel() const {
+      return static_cast<TrieEdge*>(&Sentinel);
+    }
+    void destroySentinel(TrieEdge *) const {}
+
+    TrieEdge *provideInitialHead() const { return createSentinel(); }
+    TrieEdge *ensureHead(TrieEdge*) const { return createSentinel(); }
+    static void noteHead(TrieEdge*, TrieEdge*) {}
+    void deleteNode(TrieEdge *N) {}
+
+  private:
+    void createNode(const TrieEdge &);
+  };
+} // namespace llvm
+
+
+namespace lld {
+namespace mach_o {
+namespace normalized {
+
+struct TrieNode {
+  typedef llvm::ilist<TrieEdge> TrieEdgeList;
+
+  TrieNode(StringRef s)
+      : _cummulativeString(s), _address(0), _flags(0), _other(0),
+        _trieOffset(0), _hasExportInfo(false) {}
+  ~TrieNode() = default;
+
+  void addSymbol(const Export &entry, BumpPtrAllocator &allocator,
+                 std::vector<TrieNode *> &allNodes);
+  bool updateOffset(uint32_t &offset);
+  void appendToByteBuffer(ByteBuffer &out);
+
+private:
+  StringRef                 _cummulativeString;
+  TrieEdgeList              _children;
+  uint64_t                  _address;
+  uint64_t                  _flags;
+  uint64_t                  _other;
+  StringRef                 _importedName;
+  uint32_t                  _trieOffset;
+  bool                      _hasExportInfo;
+};
+
+/// Utility class for writing a mach-o binary file given an in-memory
+/// normalized file.
+class MachOFileLayout {
+public:
+  /// All layout computation is done in the constructor.
+  MachOFileLayout(const NormalizedFile &file);
+
+  /// Returns the final file size as computed in the constructor.
+  size_t      size() const;
+
+  // Returns size of the mach_header and load commands.
+  size_t      headerAndLoadCommandsSize() const;
+
+  /// Writes the normalized file as a binary mach-o file to the specified
+  /// path.  This does not have a stream interface because the generated
+  /// file may need the 'x' bit set.
+  llvm::Error writeBinary(StringRef path);
+
+private:
+  uint32_t    loadCommandsSize(uint32_t &count);
+  void        buildFileOffsets();
+  void        writeMachHeader();
+  llvm::Error writeLoadCommands();
+  void        writeSectionContent();
+  void        writeRelocations();
+  void        writeSymbolTable();
+  void        writeRebaseInfo();
+  void        writeBindingInfo();
+  void        writeLazyBindingInfo();
+  void        writeExportInfo();
+  void        writeFunctionStartsInfo();
+  void        writeDataInCodeInfo();
+  void        writeLinkEditContent();
+  void        buildLinkEditInfo();
+  void        buildRebaseInfo();
+  void        buildBindInfo();
+  void        buildLazyBindInfo();
+  void        buildExportTrie();
+  void        computeFunctionStartsSize();
+  void        computeDataInCodeSize();
+  void        computeSymbolTableSizes();
+  void        buildSectionRelocations();
+  void        appendSymbols(const std::vector<Symbol> &symbols,
+                                      uint32_t &symOffset, uint32_t &strOffset);
+  uint32_t    indirectSymbolIndex(const Section &sect, uint32_t &index);
+  uint32_t    indirectSymbolElementSize(const Section &sect);
+
+  // For use as template parameter to load command methods.
+  struct MachO64Trait {
+    typedef llvm::MachO::segment_command_64 command;
+    typedef llvm::MachO::section_64         section;
+    enum { LC = llvm::MachO::LC_SEGMENT_64 };
+  };
+
+  // For use as template parameter to load command methods.
+  struct MachO32Trait {
+    typedef llvm::MachO::segment_command   command;
+    typedef llvm::MachO::section           section;
+    enum { LC = llvm::MachO::LC_SEGMENT };
+  };
+
+  template <typename T>
+  llvm::Error writeSingleSegmentLoadCommand(uint8_t *&lc);
+  template <typename T> llvm::Error writeSegmentLoadCommands(uint8_t *&lc);
+
+  uint32_t pointerAlign(uint32_t value);
+  static StringRef dyldPath();
+
+  struct SegExtraInfo {
+    uint32_t                    fileOffset;
+    uint32_t                    fileSize;
+    std::vector<const Section*> sections;
+  };
+  typedef std::map<const Segment*, SegExtraInfo> SegMap;
+  struct SectionExtraInfo {
+    uint32_t                    fileOffset;
+  };
+  typedef std::map<const Section*, SectionExtraInfo> SectionMap;
+
+  const NormalizedFile &_file;
+  std::error_code _ec;
+  uint8_t              *_buffer;
+  const bool            _is64;
+  const bool            _swap;
+  const bool            _bigEndianArch;
+  uint64_t              _seg1addr;
+  uint32_t              _startOfLoadCommands;
+  uint32_t              _countOfLoadCommands;
+  uint32_t              _endOfLoadCommands;
+  uint32_t              _startOfRelocations;
+  uint32_t              _startOfFunctionStarts;
+  uint32_t              _startOfDataInCode;
+  uint32_t              _startOfSymbols;
+  uint32_t              _startOfIndirectSymbols;
+  uint32_t              _startOfSymbolStrings;
+  uint32_t              _endOfSymbolStrings;
+  uint32_t              _symbolTableLocalsStartIndex;
+  uint32_t              _symbolTableGlobalsStartIndex;
+  uint32_t              _symbolTableUndefinesStartIndex;
+  uint32_t              _symbolStringPoolSize;
+  uint32_t              _symbolTableSize;
+  uint32_t              _functionStartsSize;
+  uint32_t              _dataInCodeSize;
+  uint32_t              _indirectSymbolTableCount;
+  // Used in object file creation only
+  uint32_t              _startOfSectionsContent;
+  uint32_t              _endOfSectionsContent;
+  // Used in final linked image only
+  uint32_t              _startOfLinkEdit;
+  uint32_t              _startOfRebaseInfo;
+  uint32_t              _endOfRebaseInfo;
+  uint32_t              _startOfBindingInfo;
+  uint32_t              _endOfBindingInfo;
+  uint32_t              _startOfLazyBindingInfo;
+  uint32_t              _endOfLazyBindingInfo;
+  uint32_t              _startOfExportTrie;
+  uint32_t              _endOfExportTrie;
+  uint32_t              _endOfLinkEdit;
+  uint64_t              _addressOfLinkEdit;
+  SegMap                _segInfo;
+  SectionMap            _sectInfo;
+  ByteBuffer            _rebaseInfo;
+  ByteBuffer            _bindingInfo;
+  ByteBuffer            _lazyBindingInfo;
+  ByteBuffer            _weakBindingInfo;
+  ByteBuffer            _exportTrie;
+};
+
+size_t headerAndLoadCommandsSize(const NormalizedFile &file) {
+  MachOFileLayout layout(file);
+  return layout.headerAndLoadCommandsSize();
+}
+
+StringRef MachOFileLayout::dyldPath() {
+  return "/usr/lib/dyld";
+}
+
+uint32_t MachOFileLayout::pointerAlign(uint32_t value) {
+  return llvm::alignTo(value, _is64 ? 8 : 4);
+}
+
+
+size_t MachOFileLayout::headerAndLoadCommandsSize() const {
+  return _endOfLoadCommands;
+}
+
+MachOFileLayout::MachOFileLayout(const NormalizedFile &file)
+    : _file(file),
+      _is64(MachOLinkingContext::is64Bit(file.arch)),
+      _swap(!MachOLinkingContext::isHostEndian(file.arch)),
+      _bigEndianArch(MachOLinkingContext::isBigEndian(file.arch)),
+      _seg1addr(INT64_MAX) {
+  _startOfLoadCommands = _is64 ? sizeof(mach_header_64) : sizeof(mach_header);
+  const size_t segCommandBaseSize =
+          (_is64 ? sizeof(segment_command_64) : sizeof(segment_command));
+  const size_t sectsSize = (_is64 ? sizeof(section_64) : sizeof(section));
+  if (file.fileType == llvm::MachO::MH_OBJECT) {
+    // object files have just one segment load command containing all sections
+    _endOfLoadCommands = _startOfLoadCommands
+                               + segCommandBaseSize
+                               + file.sections.size() * sectsSize
+                               + sizeof(symtab_command);
+    _countOfLoadCommands = 2;
+    if (file.hasMinVersionLoadCommand) {
+      _endOfLoadCommands += sizeof(version_min_command);
+      _countOfLoadCommands++;
+    }
+    if (!_file.functionStarts.empty()) {
+      _endOfLoadCommands += sizeof(linkedit_data_command);
+      _countOfLoadCommands++;
+    }
+    if (_file.generateDataInCodeLoadCommand) {
+      _endOfLoadCommands += sizeof(linkedit_data_command);
+      _countOfLoadCommands++;
+    }
+    // Assign file offsets to each section.
+    _startOfSectionsContent = _endOfLoadCommands;
+    unsigned relocCount = 0;
+    uint64_t offset = _startOfSectionsContent;
+    for (const Section &sect : file.sections) {
+      if (isZeroFillSection(sect.type))
+        _sectInfo[&sect].fileOffset = 0;
+      else {
+        offset = llvm::alignTo(offset, sect.alignment);
+        _sectInfo[&sect].fileOffset = offset;
+        offset += sect.content.size();
+      }
+      relocCount += sect.relocations.size();
+    }
+    _endOfSectionsContent = offset;
+
+    computeSymbolTableSizes();
+    computeFunctionStartsSize();
+    computeDataInCodeSize();
+
+    // Align start of relocations.
+    _startOfRelocations = pointerAlign(_endOfSectionsContent);
+    _startOfFunctionStarts = _startOfRelocations + relocCount * 8;
+    _startOfDataInCode = _startOfFunctionStarts + _functionStartsSize;
+    _startOfSymbols = _startOfDataInCode + _dataInCodeSize;
+    // Add Indirect symbol table.
+    _startOfIndirectSymbols = _startOfSymbols + _symbolTableSize;
+    // Align start of symbol table and symbol strings.
+    _startOfSymbolStrings = _startOfIndirectSymbols
+                  + pointerAlign(_indirectSymbolTableCount * sizeof(uint32_t));
+    _endOfSymbolStrings = _startOfSymbolStrings
+                          + pointerAlign(_symbolStringPoolSize);
+    _endOfLinkEdit = _endOfSymbolStrings;
+    DEBUG_WITH_TYPE("MachOFileLayout",
+                  llvm::dbgs() << "MachOFileLayout()\n"
+      << "  startOfLoadCommands=" << _startOfLoadCommands << "\n"
+      << "  countOfLoadCommands=" << _countOfLoadCommands << "\n"
+      << "  endOfLoadCommands=" << _endOfLoadCommands << "\n"
+      << "  startOfRelocations=" << _startOfRelocations << "\n"
+      << "  startOfSymbols=" << _startOfSymbols << "\n"
+      << "  startOfSymbolStrings=" << _startOfSymbolStrings << "\n"
+      << "  endOfSymbolStrings=" << _endOfSymbolStrings << "\n"
+      << "  startOfSectionsContent=" << _startOfSectionsContent << "\n"
+      << "  endOfSectionsContent=" << _endOfSectionsContent << "\n");
+  } else {
+    // Final linked images have one load command per segment.
+    _endOfLoadCommands = _startOfLoadCommands
+                          + loadCommandsSize(_countOfLoadCommands);
+
+    // Assign section file offsets.
+    buildFileOffsets();
+    buildLinkEditInfo();
+
+    // LINKEDIT of final linked images has in order:
+    // rebase info, binding info, lazy binding info, weak binding info,
+    // data-in-code, symbol table, indirect symbol table, symbol table strings.
+    _startOfRebaseInfo = _startOfLinkEdit;
+    _endOfRebaseInfo = _startOfRebaseInfo + _rebaseInfo.size();
+    _startOfBindingInfo = _endOfRebaseInfo;
+    _endOfBindingInfo = _startOfBindingInfo + _bindingInfo.size();
+    _startOfLazyBindingInfo = _endOfBindingInfo;
+    _endOfLazyBindingInfo = _startOfLazyBindingInfo + _lazyBindingInfo.size();
+    _startOfExportTrie = _endOfLazyBindingInfo;
+    _endOfExportTrie = _startOfExportTrie + _exportTrie.size();
+    _startOfFunctionStarts = _endOfExportTrie;
+    _startOfDataInCode = _startOfFunctionStarts + _functionStartsSize;
+    _startOfSymbols = _startOfDataInCode + _dataInCodeSize;
+    _startOfIndirectSymbols = _startOfSymbols + _symbolTableSize;
+    _startOfSymbolStrings = _startOfIndirectSymbols
+                  + pointerAlign(_indirectSymbolTableCount * sizeof(uint32_t));
+    _endOfSymbolStrings = _startOfSymbolStrings
+                          + pointerAlign(_symbolStringPoolSize);
+    _endOfLinkEdit = _endOfSymbolStrings;
+    DEBUG_WITH_TYPE("MachOFileLayout",
+                  llvm::dbgs() << "MachOFileLayout()\n"
+      << "  startOfLoadCommands=" << _startOfLoadCommands << "\n"
+      << "  countOfLoadCommands=" << _countOfLoadCommands << "\n"
+      << "  endOfLoadCommands=" << _endOfLoadCommands << "\n"
+      << "  startOfLinkEdit=" << _startOfLinkEdit << "\n"
+      << "  startOfRebaseInfo=" << _startOfRebaseInfo << "\n"
+      << "  endOfRebaseInfo=" << _endOfRebaseInfo << "\n"
+      << "  startOfBindingInfo=" << _startOfBindingInfo << "\n"
+      << "  endOfBindingInfo=" << _endOfBindingInfo << "\n"
+      << "  startOfLazyBindingInfo=" << _startOfLazyBindingInfo << "\n"
+      << "  endOfLazyBindingInfo=" << _endOfLazyBindingInfo << "\n"
+      << "  startOfExportTrie=" << _startOfExportTrie << "\n"
+      << "  endOfExportTrie=" << _endOfExportTrie << "\n"
+      << "  startOfFunctionStarts=" << _startOfFunctionStarts << "\n"
+      << "  startOfDataInCode=" << _startOfDataInCode << "\n"
+      << "  startOfSymbols=" << _startOfSymbols << "\n"
+      << "  startOfSymbolStrings=" << _startOfSymbolStrings << "\n"
+      << "  endOfSymbolStrings=" << _endOfSymbolStrings << "\n"
+      << "  addressOfLinkEdit=" << _addressOfLinkEdit << "\n");
+  }
+}
+
+uint32_t MachOFileLayout::loadCommandsSize(uint32_t &count) {
+  uint32_t size = 0;
+  count = 0;
+
+  const size_t segCommandSize =
+          (_is64 ? sizeof(segment_command_64) : sizeof(segment_command));
+  const size_t sectionSize = (_is64 ? sizeof(section_64) : sizeof(section));
+
+  // Add LC_SEGMENT for each segment.
+  size += _file.segments.size() * segCommandSize;
+  count += _file.segments.size();
+  // Add section record for each section.
+  size += _file.sections.size() * sectionSize;
+
+  // If creating a dylib, add LC_ID_DYLIB.
+  if (_file.fileType == llvm::MachO::MH_DYLIB) {
+    size += sizeof(dylib_command) + pointerAlign(_file.installName.size() + 1);
+    ++count;
+  }
+
+  // Add LC_DYLD_INFO
+  size += sizeof(dyld_info_command);
+  ++count;
+
+  // Add LC_SYMTAB
+  size += sizeof(symtab_command);
+  ++count;
+
+  // Add LC_DYSYMTAB
+  if (_file.fileType != llvm::MachO::MH_PRELOAD) {
+    size += sizeof(dysymtab_command);
+    ++count;
+  }
+
+  // If main executable add LC_LOAD_DYLINKER
+  if (_file.fileType == llvm::MachO::MH_EXECUTE) {
+    size += pointerAlign(sizeof(dylinker_command) + dyldPath().size()+1);
+    ++count;
+  }
+
+  // Add LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS, LC_VERSION_MIN_WATCHOS,
+  // LC_VERSION_MIN_TVOS
+  if (_file.hasMinVersionLoadCommand) {
+    size += sizeof(version_min_command);
+    ++count;
+  }
+
+  // Add LC_SOURCE_VERSION
+  size += sizeof(source_version_command);
+  ++count;
+
+  // If main executable add LC_MAIN
+  if (_file.fileType == llvm::MachO::MH_EXECUTE) {
+    size += sizeof(entry_point_command);
+    ++count;
+  }
+
+  // Add LC_LOAD_DYLIB for each dependent dylib.
+  for (const DependentDylib &dep : _file.dependentDylibs) {
+    size += sizeof(dylib_command) + pointerAlign(dep.path.size()+1);
+    ++count;
+  }
+
+  // Add LC_RPATH
+  for (const StringRef &path : _file.rpaths) {
+    size += pointerAlign(sizeof(rpath_command) + path.size() + 1);
+    ++count;
+  }
+
+  // Add LC_FUNCTION_STARTS if needed
+  if (!_file.functionStarts.empty()) {
+    size += sizeof(linkedit_data_command);
+    ++count;
+  }
+
+  // Add LC_DATA_IN_CODE if requested.  Note, we do encode zero length entries.
+  // FIXME: Zero length entries is only to match ld64.  Should we change this?
+  if (_file.generateDataInCodeLoadCommand) {
+    size += sizeof(linkedit_data_command);
+    ++count;
+  }
+
+  return size;
+}
+
+static bool overlaps(const Segment &s1, const Segment &s2) {
+  if (s2.address >= s1.address+s1.size)
+    return false;
+  if (s1.address >= s2.address+s2.size)
+    return false;
+  return true;
+}
+
+static bool overlaps(const Section &s1, const Section &s2) {
+  if (s2.address >= s1.address+s1.content.size())
+    return false;
+  if (s1.address >= s2.address+s2.content.size())
+    return false;
+  return true;
+}
+
+void MachOFileLayout::buildFileOffsets() {
+  // Verify no segments overlap
+  for (const Segment &sg1 : _file.segments) {
+    for (const Segment &sg2 : _file.segments) {
+      if (&sg1 == &sg2)
+        continue;
+      if (overlaps(sg1,sg2)) {
+        _ec = make_error_code(llvm::errc::executable_format_error);
+        return;
+      }
+    }
+  }
+
+  // Verify no sections overlap
+  for (const Section &s1 : _file.sections) {
+    for (const Section &s2 : _file.sections) {
+      if (&s1 == &s2)
+        continue;
+      if (overlaps(s1,s2)) {
+        _ec = make_error_code(llvm::errc::executable_format_error);
+        return;
+      }
+    }
+  }
+
+  // Build side table of extra info about segments and sections.
+  SegExtraInfo t;
+  t.fileOffset = 0;
+  for (const Segment &sg : _file.segments) {
+    _segInfo[&sg] = t;
+  }
+  SectionExtraInfo t2;
+  t2.fileOffset = 0;
+  // Assign sections to segments.
+  for (const Section &s : _file.sections) {
+    _sectInfo[&s] = t2;
+    bool foundSegment = false;
+    for (const Segment &sg : _file.segments) {
+      if (sg.name.equals(s.segmentName)) {
+        if ((s.address >= sg.address)
+                        && (s.address+s.content.size() <= sg.address+sg.size)) {
+          _segInfo[&sg].sections.push_back(&s);
+          foundSegment = true;
+          break;
+        }
+      }
+    }
+    if (!foundSegment) {
+      _ec = make_error_code(llvm::errc::executable_format_error);
+      return;
+    }
+  }
+
+  // Assign file offsets.
+  uint32_t fileOffset = 0;
+  DEBUG_WITH_TYPE("MachOFileLayout",
+                  llvm::dbgs() << "buildFileOffsets()\n");
+  for (const Segment &sg : _file.segments) {
+    _segInfo[&sg].fileOffset = fileOffset;
+    if ((_seg1addr == INT64_MAX) && sg.init_access)
+      _seg1addr = sg.address;
+    DEBUG_WITH_TYPE("MachOFileLayout",
+                  llvm::dbgs() << "  segment=" << sg.name
+                  << ", fileOffset=" << _segInfo[&sg].fileOffset << "\n");
+
+    uint32_t segFileSize = 0;
+    // A segment that is not zero-fill must use a least one page of disk space.
+    if (sg.init_access)
+      segFileSize = _file.pageSize;
+    for (const Section *s : _segInfo[&sg].sections) {
+      uint32_t sectOffset = s->address - sg.address;
+      uint32_t sectFileSize =
+        isZeroFillSection(s->type) ? 0 : s->content.size();
+      segFileSize = std::max(segFileSize, sectOffset + sectFileSize);
+
+      _sectInfo[s].fileOffset = _segInfo[&sg].fileOffset + sectOffset;
+      DEBUG_WITH_TYPE("MachOFileLayout",
+                  llvm::dbgs() << "    section=" << s->sectionName
+                  << ", fileOffset=" << fileOffset << "\n");
+    }
+
+    // round up all segments to page aligned, except __LINKEDIT
+    if (!sg.name.equals("__LINKEDIT")) {
+      _segInfo[&sg].fileSize = llvm::alignTo(segFileSize, _file.pageSize);
+      fileOffset = llvm::alignTo(fileOffset + segFileSize, _file.pageSize);
+    }
+    _addressOfLinkEdit = sg.address + sg.size;
+  }
+  _startOfLinkEdit = fileOffset;
+}
+
+size_t MachOFileLayout::size() const {
+  return _endOfSymbolStrings;
+}
+
+void MachOFileLayout::writeMachHeader() {
+  auto cpusubtype = MachOLinkingContext::cpuSubtypeFromArch(_file.arch);
+  // dynamic x86 executables on newer OS version should also set the
+  // CPU_SUBTYPE_LIB64 mask in the CPU subtype.
+  // FIXME: Check that this is a dynamic executable, not a static one.
+  if (_file.fileType == llvm::MachO::MH_EXECUTE &&
+      cpusubtype == CPU_SUBTYPE_X86_64_ALL &&
+      _file.os == MachOLinkingContext::OS::macOSX) {
+    uint32_t version;
+    bool failed = MachOLinkingContext::parsePackedVersion("10.5", version);
+    if (!failed && _file.minOSverson >= version)
+      cpusubtype |= CPU_SUBTYPE_LIB64;
+  }
+
+  mach_header *mh = reinterpret_cast<mach_header*>(_buffer);
+  mh->magic = _is64 ? llvm::MachO::MH_MAGIC_64 : llvm::MachO::MH_MAGIC;
+  mh->cputype =  MachOLinkingContext::cpuTypeFromArch(_file.arch);
+  mh->cpusubtype = cpusubtype;
+  mh->filetype = _file.fileType;
+  mh->ncmds = _countOfLoadCommands;
+  mh->sizeofcmds = _endOfLoadCommands - _startOfLoadCommands;
+  mh->flags = _file.flags;
+  if (_swap)
+    swapStruct(*mh);
+}
+
+uint32_t MachOFileLayout::indirectSymbolIndex(const Section &sect,
+                                                   uint32_t &index) {
+  if (sect.indirectSymbols.empty())
+    return 0;
+  uint32_t result = index;
+  index += sect.indirectSymbols.size();
+  return result;
+}
+
+uint32_t MachOFileLayout::indirectSymbolElementSize(const Section &sect) {
+  if (sect.indirectSymbols.empty())
+    return 0;
+  if (sect.type != S_SYMBOL_STUBS)
+    return 0;
+  return sect.content.size() / sect.indirectSymbols.size();
+}
+
+template <typename T>
+llvm::Error MachOFileLayout::writeSingleSegmentLoadCommand(uint8_t *&lc) {
+  typename T::command* seg = reinterpret_cast<typename T::command*>(lc);
+  seg->cmd = T::LC;
+  seg->cmdsize = sizeof(typename T::command)
+                          + _file.sections.size() * sizeof(typename T::section);
+  uint8_t *next = lc + seg->cmdsize;
+  memset(seg->segname, 0, 16);
+  seg->vmaddr = 0;
+  seg->vmsize = _file.sections.back().address
+              + _file.sections.back().content.size();
+  seg->fileoff = _endOfLoadCommands;
+  seg->filesize = seg->vmsize;
+  seg->maxprot = VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE;
+  seg->initprot = VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE;
+  seg->nsects = _file.sections.size();
+  seg->flags = 0;
+  if (_swap)
+    swapStruct(*seg);
+  typename T::section *sout = reinterpret_cast<typename T::section*>
+                                              (lc+sizeof(typename T::command));
+  uint32_t relOffset = _startOfRelocations;
+  uint32_t indirectSymRunningIndex = 0;
+  for (const Section &sin : _file.sections) {
+    setString16(sin.sectionName, sout->sectname);
+    setString16(sin.segmentName, sout->segname);
+    sout->addr = sin.address;
+    sout->size = sin.content.size();
+    sout->offset = _sectInfo[&sin].fileOffset;
+    sout->align = llvm::Log2_32(sin.alignment);
+    sout->reloff = sin.relocations.empty() ? 0 : relOffset;
+    sout->nreloc = sin.relocations.size();
+    sout->flags = sin.type | sin.attributes;
+    sout->reserved1 = indirectSymbolIndex(sin, indirectSymRunningIndex);
+    sout->reserved2 = indirectSymbolElementSize(sin);
+    relOffset += sin.relocations.size() * sizeof(any_relocation_info);
+    if (_swap)
+      swapStruct(*sout);
+    ++sout;
+  }
+  lc = next;
+  return llvm::Error();
+}
+
+template <typename T>
+llvm::Error MachOFileLayout::writeSegmentLoadCommands(uint8_t *&lc) {
+  uint32_t indirectSymRunningIndex = 0;
+  for (const Segment &seg : _file.segments) {
+    // Link edit has no sections and a custom range of address, so handle it
+    // specially.
+    SegExtraInfo &segInfo = _segInfo[&seg];
+    if (seg.name.equals("__LINKEDIT")) {
+      size_t linkeditSize = _endOfLinkEdit - _startOfLinkEdit;
+      typename T::command* cmd = reinterpret_cast<typename T::command*>(lc);
+      cmd->cmd = T::LC;
+      cmd->cmdsize = sizeof(typename T::command);
+      uint8_t *next = lc + cmd->cmdsize;
+      setString16("__LINKEDIT", cmd->segname);
+      cmd->vmaddr   = _addressOfLinkEdit;
+      cmd->vmsize   = llvm::alignTo(linkeditSize, _file.pageSize);
+      cmd->fileoff  = _startOfLinkEdit;
+      cmd->filesize = linkeditSize;
+      cmd->initprot = seg.init_access;
+      cmd->maxprot  = seg.max_access;
+      cmd->nsects   = 0;
+      cmd->flags    = 0;
+      if (_swap)
+        swapStruct(*cmd);
+      lc = next;
+      continue;
+    }
+    // Write segment command with trailing sections.
+    typename T::command* cmd = reinterpret_cast<typename T::command*>(lc);
+    cmd->cmd = T::LC;
+    cmd->cmdsize = sizeof(typename T::command)
+                        + segInfo.sections.size() * sizeof(typename T::section);
+    uint8_t *next = lc + cmd->cmdsize;
+    setString16(seg.name, cmd->segname);
+    cmd->vmaddr   = seg.address;
+    cmd->vmsize   = seg.size;
+    cmd->fileoff  = segInfo.fileOffset;
+    cmd->filesize = segInfo.fileSize;
+    cmd->initprot = seg.init_access;
+    cmd->maxprot  = seg.max_access;
+    cmd->nsects   = segInfo.sections.size();
+    cmd->flags    = 0;
+    if (_swap)
+      swapStruct(*cmd);
+    typename T::section *sect = reinterpret_cast<typename T::section*>
+                                               (lc+sizeof(typename T::command));
+    for (const Section *section : segInfo.sections) {
+      setString16(section->sectionName, sect->sectname);
+      setString16(section->segmentName, sect->segname);
+      sect->addr      = section->address;
+      sect->size      = section->content.size();
+      if (isZeroFillSection(section->type))
+        sect->offset  = 0;
+      else
+        sect->offset  = section->address - seg.address + segInfo.fileOffset;
+      sect->align     = llvm::Log2_32(section->alignment);
+      sect->reloff    = 0;
+      sect->nreloc    = 0;
+      sect->flags     = section->type | section->attributes;
+      sect->reserved1 = indirectSymbolIndex(*section, indirectSymRunningIndex);
+      sect->reserved2 = indirectSymbolElementSize(*section);
+      if (_swap)
+        swapStruct(*sect);
+      ++sect;
+    }
+    lc = reinterpret_cast<uint8_t*>(next);
+  }
+  return llvm::Error();
+}
+
+static void writeVersionMinLoadCommand(const NormalizedFile &_file,
+                                       bool _swap,
+                                       uint8_t *&lc) {
+  if (!_file.hasMinVersionLoadCommand)
+    return;
+  version_min_command *vm = reinterpret_cast<version_min_command*>(lc);
+  switch (_file.os) {
+    case MachOLinkingContext::OS::unknown:
+      vm->cmd     = _file.minOSVersionKind;
+      vm->cmdsize = sizeof(version_min_command);
+      vm->version = _file.minOSverson;
+      vm->sdk     = 0;
+      break;
+    case MachOLinkingContext::OS::macOSX:
+      vm->cmd     = LC_VERSION_MIN_MACOSX;
+      vm->cmdsize = sizeof(version_min_command);
+      vm->version = _file.minOSverson;
+      vm->sdk     = _file.sdkVersion;
+      break;
+    case MachOLinkingContext::OS::iOS:
+    case MachOLinkingContext::OS::iOS_simulator:
+      vm->cmd     = LC_VERSION_MIN_IPHONEOS;
+      vm->cmdsize = sizeof(version_min_command);
+      vm->version = _file.minOSverson;
+      vm->sdk     = _file.sdkVersion;
+      break;
+  }
+  if (_swap)
+    swapStruct(*vm);
+  lc += sizeof(version_min_command);
+}
+
+llvm::Error MachOFileLayout::writeLoadCommands() {
+  uint8_t *lc = &_buffer[_startOfLoadCommands];
+  if (_file.fileType == llvm::MachO::MH_OBJECT) {
+    // Object files have one unnamed segment which holds all sections.
+    if (_is64) {
+     if (auto ec = writeSingleSegmentLoadCommand<MachO64Trait>(lc))
+       return ec;
+    } else {
+      if (auto ec = writeSingleSegmentLoadCommand<MachO32Trait>(lc))
+        return ec;
+    }
+    // Add LC_SYMTAB with symbol table info
+    symtab_command* st = reinterpret_cast<symtab_command*>(lc);
+    st->cmd     = LC_SYMTAB;
+    st->cmdsize = sizeof(symtab_command);
+    st->symoff  = _startOfSymbols;
+    st->nsyms   = _file.localSymbols.size() + _file.globalSymbols.size()
+                                            + _file.undefinedSymbols.size();
+    st->stroff  = _startOfSymbolStrings;
+    st->strsize = _endOfSymbolStrings - _startOfSymbolStrings;
+    if (_swap)
+      swapStruct(*st);
+    lc += sizeof(symtab_command);
+
+    // Add LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS,
+    // LC_VERSION_MIN_WATCHOS, LC_VERSION_MIN_TVOS
+    writeVersionMinLoadCommand(_file, _swap, lc);
+
+    // Add LC_FUNCTION_STARTS if needed.
+    if (_functionStartsSize != 0) {
+      linkedit_data_command* dl = reinterpret_cast<linkedit_data_command*>(lc);
+      dl->cmd      = LC_FUNCTION_STARTS;
+      dl->cmdsize  = sizeof(linkedit_data_command);
+      dl->dataoff  = _startOfFunctionStarts;
+      dl->datasize = _functionStartsSize;
+      if (_swap)
+        swapStruct(*dl);
+      lc += sizeof(linkedit_data_command);
+    }
+
+    // Add LC_DATA_IN_CODE if requested.
+    if (_file.generateDataInCodeLoadCommand) {
+      linkedit_data_command* dl = reinterpret_cast<linkedit_data_command*>(lc);
+      dl->cmd      = LC_DATA_IN_CODE;
+      dl->cmdsize  = sizeof(linkedit_data_command);
+      dl->dataoff  = _startOfDataInCode;
+      dl->datasize = _dataInCodeSize;
+      if (_swap)
+        swapStruct(*dl);
+      lc += sizeof(linkedit_data_command);
+    }
+  } else {
+    // Final linked images have sections under segments.
+    if (_is64) {
+      if (auto ec = writeSegmentLoadCommands<MachO64Trait>(lc))
+        return ec;
+    } else {
+      if (auto ec = writeSegmentLoadCommands<MachO32Trait>(lc))
+        return ec;
+    }
+
+    // Add LC_ID_DYLIB command for dynamic libraries.
+    if (_file.fileType == llvm::MachO::MH_DYLIB) {
+      dylib_command *dc = reinterpret_cast<dylib_command*>(lc);
+      StringRef path = _file.installName;
+      uint32_t size = sizeof(dylib_command) + pointerAlign(path.size() + 1);
+      dc->cmd                         = LC_ID_DYLIB;
+      dc->cmdsize                     = size;
+      dc->dylib.name                  = sizeof(dylib_command); // offset
+      // needs to be some constant value different than the one in LC_LOAD_DYLIB
+      dc->dylib.timestamp             = 1;
+      dc->dylib.current_version       = _file.currentVersion;
+      dc->dylib.compatibility_version = _file.compatVersion;
+      if (_swap)
+        swapStruct(*dc);
+      memcpy(lc + sizeof(dylib_command), path.begin(), path.size());
+      lc[sizeof(dylib_command) + path.size()] = '\0';
+      lc += size;
+    }
+
+    // Add LC_DYLD_INFO_ONLY.
+    dyld_info_command* di = reinterpret_cast<dyld_info_command*>(lc);
+    di->cmd            = LC_DYLD_INFO_ONLY;
+    di->cmdsize        = sizeof(dyld_info_command);
+    di->rebase_off     = _rebaseInfo.size() ? _startOfRebaseInfo : 0;
+    di->rebase_size    = _rebaseInfo.size();
+    di->bind_off       = _bindingInfo.size() ? _startOfBindingInfo : 0;
+    di->bind_size      = _bindingInfo.size();
+    di->weak_bind_off  = 0;
+    di->weak_bind_size = 0;
+    di->lazy_bind_off  = _lazyBindingInfo.size() ? _startOfLazyBindingInfo : 0;
+    di->lazy_bind_size = _lazyBindingInfo.size();
+    di->export_off     = _exportTrie.size() ? _startOfExportTrie : 0;
+    di->export_size    = _exportTrie.size();
+    if (_swap)
+      swapStruct(*di);
+    lc += sizeof(dyld_info_command);
+
+    // Add LC_SYMTAB with symbol table info.
+    symtab_command* st = reinterpret_cast<symtab_command*>(lc);
+    st->cmd     = LC_SYMTAB;
+    st->cmdsize = sizeof(symtab_command);
+    st->symoff  = _startOfSymbols;
+    st->nsyms   = _file.localSymbols.size() + _file.globalSymbols.size()
+                                            + _file.undefinedSymbols.size();
+    st->stroff  = _startOfSymbolStrings;
+    st->strsize = _endOfSymbolStrings - _startOfSymbolStrings;
+    if (_swap)
+      swapStruct(*st);
+    lc += sizeof(symtab_command);
+
+    // Add LC_DYSYMTAB
+    if (_file.fileType != llvm::MachO::MH_PRELOAD) {
+      dysymtab_command* dst = reinterpret_cast<dysymtab_command*>(lc);
+      dst->cmd            = LC_DYSYMTAB;
+      dst->cmdsize        = sizeof(dysymtab_command);
+      dst->ilocalsym      = _symbolTableLocalsStartIndex;
+      dst->nlocalsym      = _file.localSymbols.size();
+      dst->iextdefsym     = _symbolTableGlobalsStartIndex;
+      dst->nextdefsym     = _file.globalSymbols.size();
+      dst->iundefsym      = _symbolTableUndefinesStartIndex;
+      dst->nundefsym      = _file.undefinedSymbols.size();
+      dst->tocoff         = 0;
+      dst->ntoc           = 0;
+      dst->modtaboff      = 0;
+      dst->nmodtab        = 0;
+      dst->extrefsymoff   = 0;
+      dst->nextrefsyms    = 0;
+      dst->indirectsymoff = _startOfIndirectSymbols;
+      dst->nindirectsyms  = _indirectSymbolTableCount;
+      dst->extreloff      = 0;
+      dst->nextrel        = 0;
+      dst->locreloff      = 0;
+      dst->nlocrel        = 0;
+      if (_swap)
+        swapStruct(*dst);
+      lc += sizeof(dysymtab_command);
+    }
+
+    // If main executable, add LC_LOAD_DYLINKER
+    if (_file.fileType == llvm::MachO::MH_EXECUTE) {
+      // Build LC_LOAD_DYLINKER load command.
+      uint32_t size=pointerAlign(sizeof(dylinker_command)+dyldPath().size()+1);
+      dylinker_command* dl = reinterpret_cast<dylinker_command*>(lc);
+      dl->cmd              = LC_LOAD_DYLINKER;
+      dl->cmdsize          = size;
+      dl->name             = sizeof(dylinker_command); // offset
+      if (_swap)
+        swapStruct(*dl);
+      memcpy(lc+sizeof(dylinker_command), dyldPath().data(), dyldPath().size());
+      lc[sizeof(dylinker_command)+dyldPath().size()] = '\0';
+      lc += size;
+    }
+
+    // Add LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS, LC_VERSION_MIN_WATCHOS,
+    // LC_VERSION_MIN_TVOS
+    writeVersionMinLoadCommand(_file, _swap, lc);
+
+    // Add LC_SOURCE_VERSION
+    {
+      // Note, using a temporary here to appease UB as we may not be aligned
+      // enough for a struct containing a uint64_t when emitting a 32-bit binary
+      source_version_command sv;
+      sv.cmd       = LC_SOURCE_VERSION;
+      sv.cmdsize   = sizeof(source_version_command);
+      sv.version   = _file.sourceVersion;
+      if (_swap)
+        swapStruct(sv);
+      memcpy(lc, &sv, sizeof(source_version_command));
+      lc += sizeof(source_version_command);
+    }
+
+    // If main executable, add LC_MAIN.
+    if (_file.fileType == llvm::MachO::MH_EXECUTE) {
+      // Build LC_MAIN load command.
+      // Note, using a temporary here to appease UB as we may not be aligned
+      // enough for a struct containing a uint64_t when emitting a 32-bit binary
+      entry_point_command ep;
+      ep.cmd       = LC_MAIN;
+      ep.cmdsize   = sizeof(entry_point_command);
+      ep.entryoff  = _file.entryAddress - _seg1addr;
+      ep.stacksize = _file.stackSize;
+      if (_swap)
+        swapStruct(ep);
+      memcpy(lc, &ep, sizeof(entry_point_command));
+      lc += sizeof(entry_point_command);
+    }
+
+    // Add LC_LOAD_DYLIB commands
+    for (const DependentDylib &dep : _file.dependentDylibs) {
+      dylib_command* dc = reinterpret_cast<dylib_command*>(lc);
+      uint32_t size = sizeof(dylib_command) + pointerAlign(dep.path.size()+1);
+      dc->cmd                         = dep.kind;
+      dc->cmdsize                     = size;
+      dc->dylib.name                  = sizeof(dylib_command); // offset
+      // needs to be some constant value different than the one in LC_ID_DYLIB
+      dc->dylib.timestamp             = 2;
+      dc->dylib.current_version       = dep.currentVersion;
+      dc->dylib.compatibility_version = dep.compatVersion;
+      if (_swap)
+        swapStruct(*dc);
+      memcpy(lc+sizeof(dylib_command), dep.path.begin(), dep.path.size());
+      lc[sizeof(dylib_command)+dep.path.size()] = '\0';
+      lc += size;
+    }
+
+    // Add LC_RPATH
+    for (const StringRef &path : _file.rpaths) {
+      rpath_command *rpc = reinterpret_cast<rpath_command *>(lc);
+      uint32_t size = pointerAlign(sizeof(rpath_command) + path.size() + 1);
+      rpc->cmd                         = LC_RPATH;
+      rpc->cmdsize                     = size;
+      rpc->path                        = sizeof(rpath_command); // offset
+      if (_swap)
+        swapStruct(*rpc);
+      memcpy(lc+sizeof(rpath_command), path.begin(), path.size());
+      lc[sizeof(rpath_command)+path.size()] = '\0';
+      lc += size;
+    }
+
+    // Add LC_FUNCTION_STARTS if needed.
+    if (_functionStartsSize != 0) {
+      linkedit_data_command* dl = reinterpret_cast<linkedit_data_command*>(lc);
+      dl->cmd      = LC_FUNCTION_STARTS;
+      dl->cmdsize  = sizeof(linkedit_data_command);
+      dl->dataoff  = _startOfFunctionStarts;
+      dl->datasize = _functionStartsSize;
+      if (_swap)
+        swapStruct(*dl);
+      lc += sizeof(linkedit_data_command);
+    }
+
+    // Add LC_DATA_IN_CODE if requested.
+    if (_file.generateDataInCodeLoadCommand) {
+      linkedit_data_command* dl = reinterpret_cast<linkedit_data_command*>(lc);
+      dl->cmd      = LC_DATA_IN_CODE;
+      dl->cmdsize  = sizeof(linkedit_data_command);
+      dl->dataoff  = _startOfDataInCode;
+      dl->datasize = _dataInCodeSize;
+      if (_swap)
+        swapStruct(*dl);
+      lc += sizeof(linkedit_data_command);
+    }
+  }
+  return llvm::Error();
+}
+
+void MachOFileLayout::writeSectionContent() {
+  for (const Section &s : _file.sections) {
+    // Copy all section content to output buffer.
+    if (isZeroFillSection(s.type))
+      continue;
+    if (s.content.empty())
+      continue;
+    uint32_t offset = _sectInfo[&s].fileOffset;
+    uint8_t *p = &_buffer[offset];
+    memcpy(p, &s.content[0], s.content.size());
+    p += s.content.size();
+  }
+}
+
+void MachOFileLayout::writeRelocations() {
+  uint32_t relOffset = _startOfRelocations;
+  for (Section sect : _file.sections) {
+    for (Relocation r : sect.relocations) {
+      any_relocation_info* rb = reinterpret_cast<any_relocation_info*>(
+                                                           &_buffer[relOffset]);
+      *rb = packRelocation(r, _swap, _bigEndianArch);
+      relOffset += sizeof(any_relocation_info);
+    }
+  }
+}
+
+void MachOFileLayout::appendSymbols(const std::vector<Symbol> &symbols,
+                                   uint32_t &symOffset, uint32_t &strOffset) {
+  for (const Symbol &sym : symbols) {
+    if (_is64) {
+      nlist_64* nb = reinterpret_cast<nlist_64*>(&_buffer[symOffset]);
+      nb->n_strx = strOffset - _startOfSymbolStrings;
+      nb->n_type = sym.type | sym.scope;
+      nb->n_sect = sym.sect;
+      nb->n_desc = sym.desc;
+      nb->n_value = sym.value;
+      if (_swap)
+        swapStruct(*nb);
+      symOffset += sizeof(nlist_64);
+    } else {
+      nlist* nb = reinterpret_cast<nlist*>(&_buffer[symOffset]);
+      nb->n_strx = strOffset - _startOfSymbolStrings;
+      nb->n_type = sym.type | sym.scope;
+      nb->n_sect = sym.sect;
+      nb->n_desc = sym.desc;
+      nb->n_value = sym.value;
+      if (_swap)
+        swapStruct(*nb);
+      symOffset += sizeof(nlist);
+    }
+    memcpy(&_buffer[strOffset], sym.name.begin(), sym.name.size());
+    strOffset += sym.name.size();
+    _buffer[strOffset++] ='\0'; // Strings in table have nul terminator.
+  }
+}
+
+void MachOFileLayout::writeFunctionStartsInfo() {
+  if (!_functionStartsSize)
+    return;
+  memcpy(&_buffer[_startOfFunctionStarts], _file.functionStarts.data(),
+         _functionStartsSize);
+}
+
+void MachOFileLayout::writeDataInCodeInfo() {
+  uint32_t offset = _startOfDataInCode;
+  for (const DataInCode &entry : _file.dataInCode) {
+    data_in_code_entry *dst = reinterpret_cast<data_in_code_entry*>(
+                                                             &_buffer[offset]);
+    dst->offset = entry.offset;
+    dst->length = entry.length;
+    dst->kind   = entry.kind;
+    if (_swap)
+      swapStruct(*dst);
+    offset += sizeof(data_in_code_entry);
+  }
+}
+
+void MachOFileLayout::writeSymbolTable() {
+  // Write symbol table and symbol strings in parallel.
+  uint32_t symOffset = _startOfSymbols;
+  uint32_t strOffset = _startOfSymbolStrings;
+  _buffer[strOffset++] = '\0'; // Reserve n_strx offset of zero to mean no name.
+  appendSymbols(_file.localSymbols, symOffset, strOffset);
+  appendSymbols(_file.globalSymbols, symOffset, strOffset);
+  appendSymbols(_file.undefinedSymbols, symOffset, strOffset);
+  // Write indirect symbol table array.
+  uint32_t *indirects = reinterpret_cast<uint32_t*>
+                                            (&_buffer[_startOfIndirectSymbols]);
+  if (_file.fileType == llvm::MachO::MH_OBJECT) {
+    // Object files have sections in same order as input normalized file.
+    for (const Section &section : _file.sections) {
+      for (uint32_t index : section.indirectSymbols) {
+        if (_swap)
+          *indirects++ = llvm::sys::getSwappedBytes(index);
+        else
+          *indirects++ = index;
+      }
+    }
+  } else {
+    // Final linked images must sort sections from normalized file.
+    for (const Segment &seg : _file.segments) {
+      SegExtraInfo &segInfo = _segInfo[&seg];
+      for (const Section *section : segInfo.sections) {
+        for (uint32_t index : section->indirectSymbols) {
+          if (_swap)
+            *indirects++ = llvm::sys::getSwappedBytes(index);
+          else
+            *indirects++ = index;
+        }
+      }
+    }
+  }
+}
+
+void MachOFileLayout::writeRebaseInfo() {
+  memcpy(&_buffer[_startOfRebaseInfo], _rebaseInfo.bytes(), _rebaseInfo.size());
+}
+
+void MachOFileLayout::writeBindingInfo() {
+  memcpy(&_buffer[_startOfBindingInfo],
+                                    _bindingInfo.bytes(), _bindingInfo.size());
+}
+
+void MachOFileLayout::writeLazyBindingInfo() {
+  memcpy(&_buffer[_startOfLazyBindingInfo],
+                            _lazyBindingInfo.bytes(), _lazyBindingInfo.size());
+}
+
+void MachOFileLayout::writeExportInfo() {
+  memcpy(&_buffer[_startOfExportTrie], _exportTrie.bytes(), _exportTrie.size());
+}
+
+void MachOFileLayout::buildLinkEditInfo() {
+  buildRebaseInfo();
+  buildBindInfo();
+  buildLazyBindInfo();
+  buildExportTrie();
+  computeSymbolTableSizes();
+  computeFunctionStartsSize();
+  computeDataInCodeSize();
+}
+
+void MachOFileLayout::buildSectionRelocations() {
+
+}
+
+void MachOFileLayout::buildRebaseInfo() {
+  // TODO: compress rebasing info.
+  for (const RebaseLocation& entry : _file.rebasingInfo) {
+    _rebaseInfo.append_byte(REBASE_OPCODE_SET_TYPE_IMM | entry.kind);
+    _rebaseInfo.append_byte(REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+                            | entry.segIndex);
+    _rebaseInfo.append_uleb128(entry.segOffset);
+    _rebaseInfo.append_uleb128(REBASE_OPCODE_DO_REBASE_IMM_TIMES | 1);
+  }
+  _rebaseInfo.append_byte(REBASE_OPCODE_DONE);
+  _rebaseInfo.align(_is64 ? 8 : 4);
+}
+
+void MachOFileLayout::buildBindInfo() {
+  // TODO: compress bind info.
+  uint64_t lastAddend = 0;
+  for (const BindLocation& entry : _file.bindingInfo) {
+    _bindingInfo.append_byte(BIND_OPCODE_SET_TYPE_IMM | entry.kind);
+    _bindingInfo.append_byte(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+                            | entry.segIndex);
+    _bindingInfo.append_uleb128(entry.segOffset);
+    if (entry.ordinal > 0)
+      _bindingInfo.append_byte(BIND_OPCODE_SET_DYLIB_ORDINAL_IMM |
+                               (entry.ordinal & 0xF));
+    else
+      _bindingInfo.append_byte(BIND_OPCODE_SET_DYLIB_SPECIAL_IMM |
+                               (entry.ordinal & 0xF));
+    _bindingInfo.append_byte(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM);
+    _bindingInfo.append_string(entry.symbolName);
+    if (entry.addend != lastAddend) {
+      _bindingInfo.append_byte(BIND_OPCODE_SET_ADDEND_SLEB);
+      _bindingInfo.append_sleb128(entry.addend);
+      lastAddend = entry.addend;
+    }
+    _bindingInfo.append_byte(BIND_OPCODE_DO_BIND);
+  }
+  _bindingInfo.append_byte(BIND_OPCODE_DONE);
+  _bindingInfo.align(_is64 ? 8 : 4);
+}
+
+void MachOFileLayout::buildLazyBindInfo() {
+  for (const BindLocation& entry : _file.lazyBindingInfo) {
+    _lazyBindingInfo.append_byte(BIND_OPCODE_SET_TYPE_IMM | entry.kind);
+    _lazyBindingInfo.append_byte(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+                            | entry.segIndex);
+    _lazyBindingInfo.append_uleb128Fixed(entry.segOffset, 5);
+    if (entry.ordinal > 0)
+      _lazyBindingInfo.append_byte(BIND_OPCODE_SET_DYLIB_ORDINAL_IMM |
+                                   (entry.ordinal & 0xF));
+    else
+      _lazyBindingInfo.append_byte(BIND_OPCODE_SET_DYLIB_SPECIAL_IMM |
+                                   (entry.ordinal & 0xF));
+    _lazyBindingInfo.append_byte(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM);
+    _lazyBindingInfo.append_string(entry.symbolName);
+    _lazyBindingInfo.append_byte(BIND_OPCODE_DO_BIND);
+    _lazyBindingInfo.append_byte(BIND_OPCODE_DONE);
+  }
+  _lazyBindingInfo.append_byte(BIND_OPCODE_DONE);
+  _lazyBindingInfo.align(_is64 ? 8 : 4);
+}
+
+void TrieNode::addSymbol(const Export& entry,
+                         BumpPtrAllocator &allocator,
+                         std::vector<TrieNode*> &allNodes) {
+  StringRef partialStr = entry.name.drop_front(_cummulativeString.size());
+  for (TrieEdge &edge : _children) {
+    StringRef edgeStr = edge._subString;
+    if (partialStr.startswith(edgeStr)) {
+      // Already have matching edge, go down that path.
+      edge._child->addSymbol(entry, allocator, allNodes);
+      return;
+    }
+    // See if string has commmon prefix with existing edge.
+    for (int n=edgeStr.size()-1; n > 0; --n) {
+      if (partialStr.substr(0, n).equals(edgeStr.substr(0, n))) {
+        // Splice in new node:  was A -> C,  now A -> B -> C
+        StringRef bNodeStr = edge._child->_cummulativeString;
+        bNodeStr = bNodeStr.drop_back(edgeStr.size()-n).copy(allocator);
+        auto *bNode = new (allocator) TrieNode(bNodeStr);
+        allNodes.push_back(bNode);
+        TrieNode* cNode = edge._child;
+        StringRef abEdgeStr = edgeStr.substr(0,n).copy(allocator);
+        StringRef bcEdgeStr = edgeStr.substr(n).copy(allocator);
+        DEBUG_WITH_TYPE("trie-builder", llvm::dbgs()
+                        << "splice in TrieNode('" << bNodeStr
+                        << "') between edge '"
+                        << abEdgeStr << "' and edge='"
+                        << bcEdgeStr<< "'\n");
+        TrieEdge& abEdge = edge;
+        abEdge._subString = abEdgeStr;
+        abEdge._child = bNode;
+        auto *bcEdge = new (allocator) TrieEdge(bcEdgeStr, cNode);
+        bNode->_children.insert(bNode->_children.end(), bcEdge);
+        bNode->addSymbol(entry, allocator, allNodes);
+        return;
+      }
+    }
+  }
+  if (entry.flags & EXPORT_SYMBOL_FLAGS_REEXPORT) {
+    assert(entry.otherOffset != 0);
+  }
+  if (entry.flags & EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER) {
+    assert(entry.otherOffset != 0);
+  }
+  // No commonality with any existing child, make a new edge.
+  auto *newNode = new (allocator) TrieNode(entry.name.copy(allocator));
+  auto *newEdge = new (allocator) TrieEdge(partialStr, newNode);
+  _children.insert(_children.end(), newEdge);
+  DEBUG_WITH_TYPE("trie-builder", llvm::dbgs()
+                   << "new TrieNode('" << entry.name << "') with edge '"
+                   << partialStr << "' from node='"
+                   << _cummulativeString << "'\n");
+  newNode->_address = entry.offset;
+  newNode->_flags = entry.flags | entry.kind;
+  newNode->_other = entry.otherOffset;
+  if ((entry.flags & EXPORT_SYMBOL_FLAGS_REEXPORT) && !entry.otherName.empty())
+    newNode->_importedName = entry.otherName.copy(allocator);
+  newNode->_hasExportInfo = true;
+  allNodes.push_back(newNode);
+}
+
+bool TrieNode::updateOffset(uint32_t& offset) {
+  uint32_t nodeSize = 1; // Length when no export info
+  if (_hasExportInfo) {
+    if (_flags & EXPORT_SYMBOL_FLAGS_REEXPORT) {
+      nodeSize = llvm::getULEB128Size(_flags);
+      nodeSize += llvm::getULEB128Size(_other); // Other contains ordinal.
+      nodeSize += _importedName.size();
+      ++nodeSize; // Trailing zero in imported name.
+    } else {
+      nodeSize = llvm::getULEB128Size(_flags) + llvm::getULEB128Size(_address);
+      if (_flags & EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER)
+        nodeSize += llvm::getULEB128Size(_other);
+    }
+    // Overall node size so far is uleb128 of export info + actual export info.
+    nodeSize += llvm::getULEB128Size(nodeSize);
+  }
+  // Compute size of all child edges.
+  ++nodeSize; // Byte for number of chidren.
+  for (TrieEdge &edge : _children) {
+    nodeSize += edge._subString.size() + 1 // String length.
+              + llvm::getULEB128Size(edge._child->_trieOffset); // Offset len.
+  }
+  // On input, 'offset' is new prefered location for this node.
+  bool result = (_trieOffset != offset);
+  // Store new location in node object for use by parents.
+  _trieOffset = offset;
+  // Update offset for next iteration.
+  offset += nodeSize;
+  // Return true if _trieOffset was changed.
+  return result;
+}
+
+void TrieNode::appendToByteBuffer(ByteBuffer &out) {
+  if (_hasExportInfo) {
+    if (_flags & EXPORT_SYMBOL_FLAGS_REEXPORT) {
+      if (!_importedName.empty()) {
+        // nodes with re-export info: size, flags, ordinal, import-name
+        uint32_t nodeSize = llvm::getULEB128Size(_flags)
+                          + llvm::getULEB128Size(_other)
+                          + _importedName.size() + 1;
+        assert(nodeSize < 256);
+        out.append_byte(nodeSize);
+        out.append_uleb128(_flags);
+        out.append_uleb128(_other);
+        out.append_string(_importedName);
+      } else {
+        // nodes without re-export info: size, flags, ordinal, empty-string
+        uint32_t nodeSize = llvm::getULEB128Size(_flags)
+                          + llvm::getULEB128Size(_other) + 1;
+        assert(nodeSize < 256);
+        out.append_byte(nodeSize);
+        out.append_uleb128(_flags);
+        out.append_uleb128(_other);
+        out.append_byte(0);
+      }
+    } else if ( _flags & EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER ) {
+      // Nodes with export info: size, flags, address, other
+      uint32_t nodeSize = llvm::getULEB128Size(_flags)
+                        + llvm::getULEB128Size(_address)
+                        + llvm::getULEB128Size(_other);
+      assert(nodeSize < 256);
+      out.append_byte(nodeSize);
+      out.append_uleb128(_flags);
+      out.append_uleb128(_address);
+      out.append_uleb128(_other);
+    } else {
+      // Nodes with export info: size, flags, address
+      uint32_t nodeSize = llvm::getULEB128Size(_flags)
+                        + llvm::getULEB128Size(_address);
+      assert(nodeSize < 256);
+      out.append_byte(nodeSize);
+      out.append_uleb128(_flags);
+      out.append_uleb128(_address);
+    }
+  } else {
+    // Node with no export info.
+    uint32_t nodeSize = 0;
+    out.append_byte(nodeSize);
+  }
+  // Add number of children.
+  assert(_children.size() < 256);
+  out.append_byte(_children.size());
+  // Append each child edge substring and node offset.
+  for (TrieEdge &edge : _children) {
+    out.append_string(edge._subString);
+    out.append_uleb128(edge._child->_trieOffset);
+  }
+}
+
+void MachOFileLayout::buildExportTrie() {
+  if (_file.exportInfo.empty())
+    return;
+
+  // For all temporary strings and objects used building trie.
+  BumpPtrAllocator allocator;
+
+  // Build trie of all exported symbols.
+  auto *rootNode = new (allocator) TrieNode(StringRef());
+  std::vector<TrieNode*> allNodes;
+  allNodes.reserve(_file.exportInfo.size()*2);
+  allNodes.push_back(rootNode);
+  for (const Export& entry : _file.exportInfo) {
+    rootNode->addSymbol(entry, allocator, allNodes);
+  }
+
+  // Assign each node in the vector an offset in the trie stream, iterating
+  // until all uleb128 sizes have stabilized.
+  bool more;
+  do {
+    uint32_t offset = 0;
+    more = false;
+    for (TrieNode* node : allNodes) {
+      if (node->updateOffset(offset))
+        more = true;
+    }
+  } while (more);
+
+  // Serialize trie to ByteBuffer.
+  for (TrieNode* node : allNodes) {
+    node->appendToByteBuffer(_exportTrie);
+  }
+  _exportTrie.align(_is64 ? 8 : 4);
+}
+
+void MachOFileLayout::computeSymbolTableSizes() {
+  // MachO symbol tables have three ranges: locals, globals, and undefines
+  const size_t nlistSize = (_is64 ? sizeof(nlist_64) : sizeof(nlist));
+  _symbolTableSize = nlistSize * (_file.localSymbols.size()
+                                + _file.globalSymbols.size()
+                                + _file.undefinedSymbols.size());
+  _symbolStringPoolSize = 1; // Always reserve 1-byte for the empty string.
+  for (const Symbol &sym : _file.localSymbols) {
+    _symbolStringPoolSize += (sym.name.size()+1);
+  }
+  for (const Symbol &sym : _file.globalSymbols) {
+    _symbolStringPoolSize += (sym.name.size()+1);
+  }
+  for (const Symbol &sym : _file.undefinedSymbols) {
+    _symbolStringPoolSize += (sym.name.size()+1);
+  }
+  _symbolTableLocalsStartIndex = 0;
+  _symbolTableGlobalsStartIndex = _file.localSymbols.size();
+  _symbolTableUndefinesStartIndex = _symbolTableGlobalsStartIndex
+                                    + _file.globalSymbols.size();
+
+  _indirectSymbolTableCount = 0;
+  for (const Section &sect : _file.sections) {
+    _indirectSymbolTableCount += sect.indirectSymbols.size();
+  }
+}
+
+void MachOFileLayout::computeFunctionStartsSize() {
+  _functionStartsSize = _file.functionStarts.size();
+}
+
+void MachOFileLayout::computeDataInCodeSize() {
+  _dataInCodeSize = _file.dataInCode.size() * sizeof(data_in_code_entry);
+}
+
+void MachOFileLayout::writeLinkEditContent() {
+  if (_file.fileType == llvm::MachO::MH_OBJECT) {
+    writeRelocations();
+    writeFunctionStartsInfo();
+    writeDataInCodeInfo();
+    writeSymbolTable();
+  } else {
+    writeRebaseInfo();
+    writeBindingInfo();
+    writeLazyBindingInfo();
+    // TODO: add weak binding info
+    writeExportInfo();
+    writeFunctionStartsInfo();
+    writeDataInCodeInfo();
+    writeSymbolTable();
+  }
+}
+
+llvm::Error MachOFileLayout::writeBinary(StringRef path) {
+  // Check for pending error from constructor.
+  if (_ec)
+    return llvm::errorCodeToError(_ec);
+  // Create FileOutputBuffer with calculated size.
+  unsigned flags = 0;
+  if (_file.fileType != llvm::MachO::MH_OBJECT)
+    flags = llvm::FileOutputBuffer::F_executable;
+  ErrorOr<std::unique_ptr<llvm::FileOutputBuffer>> fobOrErr =
+      llvm::FileOutputBuffer::create(path, size(), flags);
+  if (std::error_code ec = fobOrErr.getError())
+    return llvm::errorCodeToError(ec);
+  std::unique_ptr<llvm::FileOutputBuffer> &fob = *fobOrErr;
+  // Write content.
+  _buffer = fob->getBufferStart();
+  writeMachHeader();
+  if (auto ec = writeLoadCommands())
+    return ec;
+  writeSectionContent();
+  writeLinkEditContent();
+  fob->commit();
+
+  return llvm::Error();
+}
+
+/// Takes in-memory normalized view and writes a mach-o object file.
+llvm::Error writeBinary(const NormalizedFile &file, StringRef path) {
+  MachOFileLayout layout(file);
+  return layout.writeBinary(path);
+}
+
+} // namespace normalized
+} // namespace mach_o
+} // namespace lld